The invention relates to a flat tube heat exchanger with more than two flows, preferably an evaporator, for motor vehicles having a deflecting (or reversing) bottom for deflecting (or reversing) adjacent flows of the flat tubes with the features of the preamble of claim 1. Such a flat tube heat exchanger with a deflecting bottom is known from the DE 195 15 528A1. In such flat tube heat exchangers, in the past either deflecting bottoms being an integral part from the beginning or, according to the prior art from which the invention departs, individual deflecting bottoms linked to one another and forming a structural unit as a whole have been used. In the past, this structure has been provided for stability reasons, and at the other ends of the flat tubes normally a cohesion is furthermore effected via the header common to the flat tubes, such that this header and the coherent deflecting bottom together form a frame-like mounting for the whole structure of the flat tube heat exchanger. This is in particular true for the pre-assembly before soldering or brazing, e.g. for preventing the zig zag fins from slipping out before being soldered or brazed.
The term header is generally not to only mean an intermediate header or a header on the outlet side, but also a distributor on the inlet side.